Stellar Populations, Bars and Secular Evolution in Late-Type Galaxies

We have done a robust statistical analysis of UBV color profiles of 257 Sbc barred and unbarred galaxies. We found that there is an excess of barred galaxies among the objects with null or positive (bluish inward) color gradients, which seems to indicate that bars act as a mechanism of homogenization of the stellar population along galaxies. Moreover, the relationship found between total and bulge colors shows that, in the process of homogenization, the stellar population of bulges are getting bluer, whereas the total color of galaxies remains the same. These characteristics are expected in a secular evolutionary scenario, and seem incompatible with both the monolithic and the hierarchical scenarios for spiral galaxy formation.Comment: 2 pages, 1 table, no figures. To appear in ASP Conference Series, "Galaxy Disks and Disk Galaxies", J. G. Funes S. J. and E. M. Corsini, ed

Massive molecular gas reservoir in a luminous submillimeter galaxy during cosmic noon

Galaxie

Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the Ultraviolet Anomaly in NGC 5548 with X-Ray Spectroscopy

During the Space Telescope and Optical Reverberation Mapping Project observations of NGC 5548, the continuum and emission-line variability became decorrelated during the second half of the six-month-long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with the Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all three observations: the UV emission-line flux decrease, the soft-excess increase, and the emission-line anomaly

Characterisation of <i>Herschel</i>-selected strong lens candidates through <i>HST</i> and sub-mm/mm observations

We have carried out HST snapshot observations at 1.1 μm of 281 candidate strongly lensed galaxies identified in the wide-area extragalactic surveys conducted with the Herschel space observatory. Our candidates comprise systems with flux densities at 500 μm S500 ≥ 80 mJy. We model and subtract the surface brightness distribution for 130 systems, where we identify a candidate for the foreground lens candidate. After combining visual inspection, archival high-resolution observations, and lens subtraction, we divide the systems into different classes according to their lensing likelihood. We confirm 65 systems to be lensed. Of these, 30 are new discoveries. We successfully perform lens modelling and source reconstruction on 23 systems, where the foreground lenses are isolated galaxies and the background sources are detected in the HST images. All the systems are successfully modelled as a singular isothermal ellipsoid. The Einstein radii of the lenses and the magnifications of the background sources are consistent with previous studies. However, the background source circularised radii (between 0.34 kpc and 1.30 kpc) are ∼3 times smaller than the ones measured in the sub-mm/mm for a similarly selected and partially overlapping sample. We compare our lenses with those in the SLACS survey, confirming that our lens-independent selection is more effective at picking up fainter and diffuse galaxies and group lenses. This sample represents the first step towards characterising the near-IR properties and stellar masses of the gravitationally lensed dusty star-forming galaxies

Dicationic μ-diborolyl arene triple-decker complexes [CpCo(μ-1,3-C&lt;inf&gt;3&lt;/inf&gt;B&lt;inf&gt;2&lt;/inf&gt;Me&lt;inf&gt;5&lt;/inf&gt;)M(arene)]&lt;sup&gt;2+&lt;/sup&gt; (M = Rh, Ir; Cp = cyclopentadienyl): Synthesis, structures, electrochemistry and bonding

The reaction of the bromide complexes [CpCo(μ-1,3-C3B2Me5)MBr2]2 [M = Rh (1), Ir (2); Cp = cyclopentadienyl] with AgBF4 in acetonitrile affords the tris(acetonitrile) μ-diborolyl triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(MeCN)3]2+ [Rh (3), Ir (4)]. The labile nitromethane solvates [CpCo(μ-1,3-C3B2Me5)M(MeNO2)3]2+, generated in a similar way, react with benzene and its methylated derivatives to give the arene triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(arene)]2+ [M = Rh (5), Ir (6); arene = C6H6 (a), 1,2,4,5-Me4C6H2 (b), C6Me6 (c)]. The structures of 5b(BF4)2, 5c(BF4)2, 6b(BF4)2 and 6c(BF4)2 were determined by X-ray diffraction. The electron-transfer ability of the arene complexes was ascertained by electrochemical techniques. In general, they are able to undergo two separate one-electron reductions reversibly. DFT calculations revealed structural changes caused by redox processes and satisfactorily predicted the redox potentials. The second reduction is accompanied by a η6-→-η4 hapticity change of the arene ligand. Energy decomposition analysis revealed that the Rh-benzene bond in cation 5a is weaker than in cyclopentadienyl analogues [(C5R5)Rh(C6H6)]2+; however, 5a proved to be the least reactive in benzene replacement with acetonitrile and mesitylene. The labile nitromethane solvates [CpCo(μ-1,3-C3B2Me5)M(MeNO2)3]2+ {generated from the bromide complexes [CpCo(μ-1,3-C3B2Me5)MBr2]2 (M = Rh, Ir; Cp = cyclopentadienyl) and AgBF4 in MeNO2} react with arenes to give triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(arene)]2+. X-ray diffraction, electrochemical techniques and DFT calculations were used for the characterization of the complexes obtaine